This application claims the benefit of Korean Application No. 2002-5865, filed Feb. 1, 2002, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates, in general, to linear compressors and, more particularly, to a linear compressor provided with an anti-collision device for preventing a piston from excessively moving past an upper dead center position of the linear compressor inside a cylinder to collide against the cylinder head having a suction valve.
2. Description of the Related Art
As well known to those skilled in the art, a compressor is a machine that sucks and compresses gas refrigerant in a refrigerating system or an air conditioning system, such as a refrigerator or an air conditioner, by performing a refrigeration cycle. Such compressors have been typically classified into three types: reciprocating compressors, rotary compressors and linear compressors. In the linear compressors, a linear motor is used as a drive unit linearly reciprocating a piston to compress gas refrigerant and is low in energy loss for the drive unit, thus being high in energy efficiency in comparison with the other types of compressors. FIG. 1 is a view, showing the construction of a conventional linear compressor.
As shown in FIG. 1, the conventional linear compressor comprises a drive unit 2 and a compressing unit 3, which are housed in a hermetic casing 1. The drive unit 2 generates drive power when supplied by electricity, while the compressing unit 3 sucks gas refrigerant and compresses the gas refrigerant using the drive power transmitted from the drive unit 2.
The compressing unit 3 comprises a cylinder block 3a having a cylinder 3b, with a cylinder head 3c assembled with a lower end of the cylinder block 3a and provided with a suction valve 8a and an exhaust valve 8b guiding inlet and outlet gas refrigerant. A piston 3d is movably received in the cylinder 3b such that the piston 3d linearly reciprocates in the cylinder 3b using the drive power transmitted from the drive unit 2.
The drive unit 2, which is a linear motor, comprises a cylindrical inside stator 4 fitted over the cylinder 3b, and a cylindrical outer stator 5 which is arranged such that the cylindrical outside stator 5 surrounds the cylindrical inside stator 4 with an annular gap defined between the two stators 4 and 5. A magnet 6 is positioned in the gap formed between the two stators 4 and 5 such that the magnet 6 vertically reciprocates in the gap.
The cylindrical outside stator 5 is fabricated by closely layering a plurality of steel sheets 5a in a radial direction, thus forming a cylindrical shape. A coil 5b is wound in the cylindrical outside stator 5, and so the cylindrical outside stator 5 generates a magnetic flux when an alternating current AC is applied to the coil 5b of the cylindrical outside stator 5. The lower end of the cylindrical outside stator 5 is seated on a first support frame 3e, which extends outward in a radial direction from a lower end of the cylinder block 3a. An upper end of the cylindrical outside stator 5 is supported by a second support frame 3f, which is assembled with the first support frame 3e using a plurality of bolts 9.
The cylindrical inner stator 4 is fabricated by regularly arranging a plurality of steel sheets 4b in a radial direction around a cylindrical holder 4a. This cylindrical inside stator 4 is positioned outside the cylinder 3b, and forms a complete electromagnetic circuit of the linear motor in combination with the cylindrical outside stator 5 having the coil 5b. 
The magnet 6 is arranged such that the magnet 6 vertically reciprocates in the gap between the two stators 4 and 5, and is connected to the piston 3d. Therefore, the piston 3d linearly reciprocates in the cylinder 3b at the same time as a linear reciprocating action of the magnet 6. A resonant spring 7, as shown in FIG. 1, is used to enhance a reciprocating force of the piston 3d. 
When the alternating current AC is applied to the coil 5b of the cylindrical outside stator 5, the coil 5b generates a magnetic flux. This magnetic flux of the coil 5b cooperates with the magnetic field of the magnet 6, thus allowing the magnet 6 and the piston 3d to reciprocate in a vertical direction at the same time.
When the piston 3d moves from a stop position to a lower dead center position, as shown by the arrow xe2x80x9cBxe2x80x9d of FIG. 1, during a reciprocating action of the piston 3d, the suction valve 8a is opened, while the exhaust valve 8b is closed. Gas refrigerant is sucked from a suction chamber into the cylinder 3b. When the piston 3d moves to the upper dead center position, as shown by the arrow xe2x80x9cAxe2x80x9d of FIG. 1, the suction valve 8a is closed, while the exhaust valve 8b is opened to discharge the compressed gas refrigerant from the hermetic casing 1.
In a conventional linear compressor, a natural frequency of the resonant spring 7, according to a mass of both the piston 3d and the magnet 6, is set to be substantially equal to a frequency of the alternating current AC applied to the coil 5b of the cylindrical outside stator 5, and the drive unit 2 can therefore generate high drive power by resonance of the piston 3d, magnet 6 and resonant spring 7. An amplitude of both the reciprocating piston 3d and the magnet 6 is regulated by controlling an applied voltage. To allow the piston 3d to stably reciprocate with a predetermined amplitude, a separate control unit (not shown) is provided, which is capable of stably controlling the amplitude of the piston 3d. 
In the conventional linear compressor, a volumetric efficiency of the compressor varies in accordance with a clearance volume determined by a minimum gap between the cylinder head 3c and the upper dead center position of the piston 3d. Accordingly, higher volumetric efficiency of the linear compressor can be obtained as the minimum gap distance is reduced. Therefore, when high volumetric efficiency of the linear compressor is desired, the clearance volume should be reduced as much as possible by controlling the amplitude of the piston 3d such that the piston 3d can closely approach the cylinder head 3c and the suction valve 8a during an operation of the linear compressor.
However, during a linear reciprocating action of the piston 3d in the cylinder 3b of the conventional linear compressor, behavior of the piston 3d may unexpectedly become unstable, thus abruptly and rapidly increasing the amplitude of the piston 3d due to unexpected internal or external causes, such as unexpected rapid variation in the applied voltage or unexpected rapid variation in a pressure of a refrigeration cycle.
When the amplitude of the piston 3d rapidly increases as described above, the end of the piston 3d may collide with the suction valve 8a and/or the cylinder head 3c, thus generating operational noise, as well as causing serious damage or breakage of the cylinder head 3c, the suction valve 8a, and/or the piston 3d. 
Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a linear compressor, which is provided with an anti-collision device for preventing a movement of a piston past an upper dead center position of the piston in a cylinder, thereby preventing the piston from colliding with a suction valve and/or a cylinder head, and attenuates impacts resulting from an excessive movement of the piston.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To accomplish the above and other objects, a linear compressor is provided, which comprises a cylinder block provided on a upper surface thereof with a cylinder receiving a piston in the cylinder while allowing the piston to linearly reciprocate in the cylinder, a cylinder head assembled with a lower surface of the cylinder block and used to guide inlet and outlet refrigerant, a movable member connected to the piston and provided with a magnet arranged around the cylinder, and a drive unit reciprocating both the piston and the movable member. The linear compressor further comprises an anti-collision device set between the upper surface of the cylinder block and an end of the movable member, and used to prevent the piston from moving past an upper dead center position of the piston and thereby preventing the piston from colliding with the cylinder head.
The anti-collision device comprises a stopper including a mounting part having a ring-shaped appearance, and mounted to the upper surface of the cylinder block; and an elastic support part integrally extending from an edge of the mounting part while being inclined upward and outward at an angle of inclination such that the elastic support part is spaced apart from the upper surface of the cylinder block with a predetermined gap, the elastic support part colliding with an end of the movable member just before the piston would otherwise collide against the cylinder head.
In the linear compressor, the drive unit comprises a stator mounted to the upper surface of the cylinder block using mounting bolts such that the stator is arranged around the cylinder, and the mounting part of the stopper is arranged between the upper surface of the cylinder block and the stator of the drive unit, and is mounted along with the stator to the upper surface of the cylinder block using the mounting bolts.
The anti-collision device may further comprise a damping member provided at the predetermined gap between the elastic support part of the stopper and the upper surface of the cylinder block.
The damping member may be made of ring-shaped rubber having a predetermined thickness, and attached to the upper surface of the cylinder block.
Alternatively, the anti-collision device may further comprise a protrusion integrally formed on the upper surface of the cylinder block such that the protrusion is positioned under the elastic support part of the stopper while leaving a gap between the upper surface of the protrusion and the elastic support part of the stopper.